The process and system for carrying out the steam/CO2 reforming chemistry to accomplish this has been patented by the author (U.S. Pat. No. 6,187,465, issued Feb. 13, 2001 and CIP U.S. Pat. No. 7,132,183, issued Nov. 7, 2006, filed Jun. 23, 2003) and deals with waste steam/CO2 reformers interfacing to fuel cells. And CIP of patent application Ser. No. 10/719,504 (examined by Ryan/Lewis) filed Nov. 21, 2003 deals with cleaning the syngas produced in waste steam/CO2 reformers interfacing to fuel cells to produce energy without poisoning their sensitive catalysts.
There is a great need to destroy a wide range of waste streams generated around the world and at the same time to convert this carbonaceous waste into useful hydrogen-rich syngas by two methods: (1) to drive a fuel cell and (2) to feed a Fischer-Tropsch unit—both to produce clean energy.
The challenge and problem with fuel cells has been their extreme sensitivity to various unknown chemical poisons at parts per million levels coming from the waste streams from harming the electrochemical catalysts of the high temperature fuel cells. By comparison Flory-Huggins catalysts in Fischer-Tropsch reactors (such as supported iron and cobalt catalysts) are much less sensitive to poisons than fuel cells and are highly exothermic.CO+2H2→1/n(—CH2—)n(l)+H2O(l)ΔH°298=−231.1 kJ/mol
Conversion of syngas to methanol using copper catalysts in the gas phase or liquid-phase catalysts are exothermic and also less sensitive to poisons.CO+2H2CH3OH(l)ΔH°298=−128.2 kJ/mol
There is syngas methanation that is highly exothermic:2CO+2H2→CH4+CO2ΔH°298=−247.3 kJ/mol
And there are many other highly exothermic reactions that can use syngas and preferably produce useful high-carbon content chemicals of commercial use.
This thermochemistry is well known (R. F. Probstein & R. E. Hicks, “Synthetic Fuels,” McGraw-Hill, N.Y., 1982, 490 pp.). And all of these highly exothermic reactors produce high-grade useful energy. So they all can convert syngas with enough exothermicity to make large amounts of electricity, steam and heat. Importantly, these exothermic reactors can substitute very well for fuel cells. Thus, it is the purpose of this patent to cover methods and process systems to convert waste to energy without burning the waste but to sequester the carbon of the waste so carbon gases are not released
The composition of the syngas was determined in detail by the author in a recently completed gas test using the Bear Creek Pilot plant where solid waste was steam/CO2 reformed to make syngas. The syngas composition is shown in Table 1 below.
TABLE 1Results from Pilot Plant Gas Test By Steam/CO2 Reforming Of SolidWasteH2Hydrogen62.71vol %COCarbon Monoxide18.57CO2Carbon Dioxide10.67CH4Methane7.58C2H6Ethane0.48C3 TO C6Propane through hexane<0.01C6H6Benzene<17ppmCOSCarbonyl Sulfide4ppmCS2Carbon Disulfide0.05ppmH2SHydrogen Sulfide<5ppmC10H8Naphthalene2.6ppbC10H7CH32-Methylnaphthalene~0.6ppbC12H8Acenaphthalene~0.4ppbC12H8ODibenzofuran0.36ppbPCDF + PCDDPolychlorinated-0.0041ppt TEQdibenzofurans + Dioxins
The pilot process configuration used to conduct these tests is described in a recent publication (T. R. Galloway, F. H. Schwartz and J. Waidl, “Hydrogen from Steam/CO2 Reforming of Waste,” Nat'l Hydrogen Assoc., Annual Hydrogen Conference 2006, Long Beach, Calif. Mar. 12-16, 2006).
What has been found experimentally was that the syngas was very rich in hydrogen and carbon monoxide and also quite pure. For fuel cells the key poisons, such as carbonyl sulfide, hydrogen sulfide, carbon disulfide, hydrogen chloride, and polychlorinated organics were identified. For Fischer-Tropsch, methanol synthesis, methanation, etc., this syngas is very acceptable.
Another important part of power recovery is to reduce the energy losses of the waste-reforming kiln. Previously covered was a process interface involving a conventional kiln, followed by a desulfurizer and a high temperature filter in the CIP of patent application Ser. No. 10/719,504 (examined by Ryan/Lewis) filed Nov. 21, 2003. The problem is that the kiln was operated at a high temperature, followed by an even higher temperature steam/CO2 reformer which is then followed by the desulfurizer and high temperature filter—all energy-inefficient from heat losses from the process units themselves and from the complex of hot process piping. Also this was expensive, as well.
Regarding Fischer-Tropsch, the challenge was to develop a process train where the Fischer-Tropsch unit could produce enough high carbon product, such as high density, unsaturated paraffin wax containing little hydrogen, so that the carbon in the waste feed would be sequestered in this product, without significant carbon emissions leaving the process anywhere else. The Fischer-Tropsch train also had to produce steam for a steam-turbo-generator to make enough electricity to drive the process plant.